[Duugu]

I would do it like this:

core.lua

function evaluate_all()
    if stuff then
        for _, v in pairs(stuff) do
            v:evaluate()
        end
    end
end

module1.lua

if not stuff then stuff = {} end -- <local stuff = stuff or {}> would work too, or?
table.insert(stuff, {
    data = {a=1, b=2},
    evaluate = function()
        if a > a then
        return a
    end
})

module2.lua

if not stuff then stuff = {} end
table.insert(stuff, {
    data = {n1="nag", n2="nagnag"},
    evaluate = function()
        if n1 == n2 then
        return "nagnagnag"
    end
})